1. Field of the Invention
The invention relates to a sight piece, in particular for skiing goggles or the like, comprising a distal and a proximal sheet joined to each other by a flexible seal and spacer element that encircles along the edge.
2. Background Art
So-called double sight pieces of the generic type have been known for a long time from skiing goggles and motorbike helmet visors. They enable varying materials to be used for the proximal and distal sheets i.e., an especially scratchproof material for the distal sheet and a material appropriate for antimist coating in the case of the proximal sheet. The enclosed air cushion also counteracts sight piece fogging.
Various techniques or injection molding have been familiar methods for the manufacture of double sight piece arrangements of the generic type. For example, the distal sheet is produced by deep drawing, with an outer edge being formed that projects from the virtual plane of the sheet; the proximal sheet is then fixed to this edge by gluing or ultrasonic welding. Deep drawing or injection molding the distal sheet is costly and the bond that originates is extraordinarily rigid. As opposed to this, sight pieces of skiing goggles need to be as elastic and flexible as possible for injuries and fragmenting to be avoided in the case of skiing accidents.
It has further been known to punch the material of the seal and spacer element from flat-spread material, in particular foam material, and then to glue the sheets together by means of an adhesive. Punching produces a considerable amount of waste and glue-bonding is rather labor-consuming.
DE 295 16 680 U 1 teaches to apply the two components of a polyurethane foam along the outer edge of a sight piece for skiing goggles in a manner numerically controlled, producing a foam strip that bears against a wearer""s face.
JP patent abstracts 11 079 797 A and 09 086 979 A disclose to mount a seal of hydrocarbon resin or partially vulcanized butyl rubber between two plane-parallel glass sheets.
Proceeding from this, it is the object of the invention to further develop a sight piece of the type mentioned at the outset in such a way that it has advantageous functional properties and an attractive optical appearance accompanied with the capability of rapid manufacture at a low cost.
According to the invention, this object is attained by the sheets being glued together by means of the seal and spacer element without utilization of additional glue.
This is preferably put into practice by the seal and spacer element consisting of a flexible silicone based sealant or of a polyurethane based sealant that is sprayed on one of the two sheets and, after placement of the second sheet, simultaneously used for gluing the sheets together.
The flexible silicone based sealant is preferably formed on the basis of a silicone rubber acetate system. Such a material is distinguished by great flexibility, which is of major importance for the residing flexibility of the composite sheets.
By advantage, the silicone based sealant has a density of approximately 1.0 g/ml and/or a Shore hardness A of approximately 20 and/or a permissible overall deformation of approximately 25 percent and/or a retroactivity greater than 98 percent.
The polyurethane based sealant advantageously has a density of approximately 1 g/cm3 and/or a hardness of approximately 1 Shore A and/or a viscosity of 10,500 mPa.
The distal sheet may, in a manner known per se, consist of cellulose propionate, cellulose acetate or polycarbonate and the proximal sight piece may consist of cellulose propionate or cellulose acetate or polycarbonate like-wise in a manner known per se.
The proximal sheet may be provided with an antimist coating on both sides. Conventional gluing techniques manage to place only a unilateral coating, which renders manufacturing at lot more complicated. The design according to the invention provides for stable bonding even with bilateral coating.
Manufacturing a sight piece according to the invention is put into practice by a method in which an encircling strand of the material of the seal and spacer element is placed by means of a nozzle on one of the two sheets that will form the later double sight piece and then, with the material still soft, the second sheet is positioned and pressed on so that, after curing, the seal and spacer element will form, having the desired shape and thickness and uniting the two sheets.
Preferably, the strand of the material that constitutes the seal and spacer element is applied by a CNC-controlled spray nozzle.
In keeping with a favorable embodiment, this may be put into practice by sight piece manufacture taking place on a turntable that rotates intermittently by 90xc2x0 such that a first sheet, in particular the distal sheet, is taken from a depot and placed on the turntable; the turntable is then rotated by 90xc2x0 into a second position; the material of the seal and spacer element is applied by means of a CNC-controlled nozzle in this second position; the turntable is then rotated by 90xc2x0 into a third position in which the second sheet, in particular the proximal sheet, is taken from a depot and placed on the soft material of the seal and spacer element by defined pressure for a defined thickness of the seal and spacer element to form; the turntable is then moved into a fourth position from which the finished sight piece is discharged into a storing depot.
Details of the invention will become apparent from the ensuing description of a preferred embodiment, taken in conjunction with the drawing.